The present invention relates to systems for providing gases (e.g., air) to a patient through a body lumen. Specific embodiments of the invention relate to endotracheal intubation.
An endotracheal tube generally comprises a cylindrical tube used as an air passage to administer oxygen, anesthetic gases and medications directly to the patient. The cylindrical tube terminates in an open distal end configured for insertion into the trachea and has an opposite open proximal end configured to be coupled to a gas source. The endotracheal tube typically has an inflatable cuff on the exterior of the cylindrical tube for forming a seal with the interior walls of the trachea. The cuff functions to occlude the trachea, which protects the trachea and lungs against aspiration of foreign substances. In particular, food, foreign bodies or digestive system contents are prevented from entering the lungs. The endotracheal tube is used primarily in surgery and in the intensive care units in patients requiring mechanical ventilation, but is also frequently used in emergency rooms and emergency in-the-field situations.
The use of tracheal tubes in the medical world is widespread both in hospitals and for at home care. Tracheal tubes are used for holding weak airways open as well as in intubation for mechanical ventilation and the direct application of oxygen therapy. Constant monitoring of the patency of these tubes is required due to the immense risks associated with failure. The mechanics of tracheal tubes in artificial ventilation are particularly important to control for patients with conditions such as quadriplegia, degenerative muscular or intellectual disorders. These patients may be unable to understand or express their distress at pain sensations associated with cuff pressure or loss of air movement.
There are two main types of intubation using tracheal tubes. Either the tube is inserted through the nose or mouth (called endotracheal intubation) and down the airway, or through an external hole in the throat called a tracheal stoma. The first of these is more common, and is used frequently in acute intensive care, operating rooms to provide anesthesia or emergency applications. Direct tracheal intubation (tracheostomy) is used when endotracheal intubation is unfeasible due to medical indications or to provide chronic mechanical ventilation to patients that require ventilatory support to breathe. This may occur in an emergency situation where the airway may not be cleared in time or for long-term patients whose trachea is damaged such that it is in danger of collapse.
In surgical procedures requiring general anesthesia, the patient is rendered unconscious by administration of anesthetic agents including drugs and/or gases. The patient is also given a muscle relaxant/paralyzing agent to minimize the patient's gagging response to the insertion of the endotracheal tube. A laryngoscope is placed in the mouth of the patient. The blade portion of the laryngoscope is used to push the tongue laterally and the intubating practitioner applies a lifting force to the laryngoscope handle in order to visualize the anatomical structures of the mouth and airway. A specific target area of the tracheal tube is the glottis, which is the opening between the vocal cords and the inlet to the trachea. The distal end of the endotracheal tube is inserted into the glottis and the inflatable cuff (balloon) is filled with air to create an airtight seal between the cuff walls and the interior walls of the trachea. This airtight seal allows for delivery of the oxygen and anesthetic gases with positive pressure directly to the air passages below the tip and the balloon.
Endotracheal intubation is one of the most common procedures performed by physicians in hospitals. Patients in the intensive care units on mechanical ventilation require this kind of procedure to have access to the airways and to have mechanical ventilation. However this life saving procedure is sometimes difficult in complicated airways. Complications may include aspiration pneumonias secondary to cuff leaks and poor clearance of secretions, as well as, difficulties with ventilation due to high pressures and in some patients with post-intubation tracheal stenosis (narrowing of the trachea in the area were the cuff of the endotracheal tube is making contact with the tracheal mucusa).
Concern about complications stemming from the use of artificial airways has been evident since these devices were first introduced into clinical practice. When MacEwen successfully performed transoral endotracheal intubation in 1878 for the relief of upper airway obstruction, he recognized the potential for complications of this procedure. His report of 4 cases includes description of adverse effects associated with the use of endotracheal tubes (ETTs), including patient discomfort, cough, mucosal congestion, and glottic edema. MacEwen's first patient actually experienced no complications from the procedure: “After the operation was finished, the tube was withdrawn, it having acted throughout without the slightest hitch.”
There are many long and short term problems associated with the use of tracheal tubes. Long-term problems include stenosis of the mucosal lining of the trachea, and permanent scarring of the airway. Stenosis, the narrowing of the airway, is caused by the pressure of the tube on the inside of the trachea, wearing away the lining and allowing bacteria to build. Scarring arises from undiagnosed or untreated tracheal stenosis as well as frequent or traumatic tube changes. This further exacerbates the problem due to hardening and swelling of the airway making patency harder to achieve.
Short-term problems can either arise through normal operation of the ventilator or tube or from complications and failures in these mechanisms. During normal usage, secretions accumulate in the lungs of the patient due to the steady flow of mucus from the distal small airways into the larger and more proximal bronchi and trachea. In patients that are intubated, this fluid must be suctioned out of the lungs to prevent mucus plugging, lung collapse and pneumonia.
The pressure limited tracheal tube cuff (PLC) (Young et al., 1999) effectively eliminates the leakage of secretions past the cuff and into the lungs. These leakages occur in between 20% and 60% of all ventilated patients and may have a mortality rate due to pneumonia and other complications as high as 25%. The apparatus involved is designed to eliminate longitudinal creases, which allow fluid to channel past the tube cuff, and was found to be very effective in trials. Secretions developed by the lungs themselves as a reaction to the foreign body will still require suctioning but this will be much reduced.
Air leaks occur when the tube is not in full contact with the walls of the airway. This limits the effectiveness of the tube, particularly for mechanically ventilated patients who often require the full predetermined volume of air to maintain adequate ventilation and acceptable oxygen levels due to a decreased capacity to absorb oxygen. Air leaks are common due to positional changes of the patient that can dramatically change both the contact area of the tube and the pressure upon the tracheal walls. This increase in pressure due to changes in patient position is the primary cause of mucosal ulceration and stenosis.
While some of the adverse events associated with endotracheal intubation are inherent consequences of airway instrumentation, rather than true complications, most of the complications are avoidable, and a great deal of research has been published on the recognition, management, and avoidance of these problems. There is a need, however, for an artificial airway system, which may assist in inhibiting many of the complications associated with current technologies.